The present invention is particularly applicable for inductively heating and quench hardening the full axial extent of a three-lobed internal bore or passage in a thin walled steel workpiece commonly known as a tripot housing used in the drive assembly of a front wheel drive vehicle and it will be described with particular reference thereto; however, the invention has broader applications and may be used for hardening the full axial extent of the wall surface of a bore irrespective of the profile or cross-sectional contour thereof and which extends within a workpiece and is open at one end but closed at its other end. Although the particular apparatus disclosed herein is designed to harden only selected axially extending segmental areas of the bore, it could be used as well to harden the total surface area of the bore.
It is well known to harden the wall surface of a bore open at both ends in a steel housing such as, for example, the wall surface of the three-lobed bore of the aforementioned tripot housing, by providing an inductor matching the three-lobed bore wall contour but generally slightly smaller in cross-sectional size than the bore to permit free passage of the inductor therethrough while establishing an inductive coupling gap between the inductor and the bore wall surface. With the housing supported with its bore extending vertically and the inductor supported in a position below the housing in alignment with the bore and energized by a high frequency electrical power supply, the inductor and housing are then moved vertically relative to one another to cause the energized inductor to pass upwardly through the bore and progressively inductively heat the bore wall surface upwardly along the length thereof from the open lower end of the bore. As the bore wall surface becomes thus progressively heated by the inductor to the selected depth, the heated wall surface is then progressively quenched to harden it by directing a quenching liquid thereagainst from a quench head located directly below the inductor and passing upwardly through the bore along with the inductor. The above described process for hardening the wall surface of an open ended three-lobed bore of a tripot housing, which is disclosed in U.S. Pat. No. 4,401,485 made of record herein, thus corresponds essentially to the standard practice employed heretofore for many years to harden the cylindrical wall surface of various open ended cylindrical bores in steel workpieces. In this latter case, moreover, it is also known to rotate the workpiece about the central axis of the cylindrical bore so that the progressing inductor and associated quench head act upon a rotating cylindrical surface to thereby provide uniform progressive heating and quench hardening of the cylindrical bore wall surface.
While the known workpiece bore wall hardening methods and apparatus as described above are entirely suitable for use where the bore is open at both ends, they are not suitable for use where the bore is open at only one end and either completely or partially closed off at its other end by an end wall of the workpiece housing, and where the bore wall is to be heated and quench hardened to substantially the inner or closed end of the bore. In such case, the end wall which closes the one end of the bore interferes with and limits upward passage of the inductor through and out of the upper end of the bore. As a result, the quench head, which is located below the inductor and which directs the quench liquid more or less laterally outward and ordinairly angled downwardly therefrom and against the bore wall, is restricted and prevented from passage through the bore completely to the inner end thereof. Thus, the quench liquid directed laterally outwardly from the quench head cannot reach and impinge against the heated innermost end portions of the bore wall located opposite and above the inductor in the limiting uppermost position of the latter in the bore, thus preventing the full completion of the bore wall hardening operation. Moreover, with such prior methods and apparatus, the innermost end portions of the bore wall are not inductively heated to the necessary depth at the end of the upward passage of the inductor into the bore so that, even if such innermost end portions of the bore wall were reached and quenched by the quench liquid, insufficient hardening of such innermost end portions of the bore wall nevertheless results.